Coalescence process using polyolefin fiber



United States Patent 3,239,452 COALESCENCE PROCESS USING PQLYOLEFINFIBER Adolph Christiaan van Beest, Amsterdam, and Gerrit Schuur, Delft,Netherlands, assignors to Shell Oil Company, New York, N.Y., acorporation of Delaware No Drawing. Filed Nov. 20, 1963, Ser. No.325,131 Claims priority, application Netherlands, Nov. 30, 1962,

86 213 10 Claims. (Cl. 208-187) This invention relates to the separationof emulsions or suspensions; and, more particularly relates to thecoalescence of acid or caustic hazes from hazy hydrocarbon oils. Evenmore particularly, the invention pertains to a process for coalescingemulsions wherein the emulsion is contacted with a polymer having aparticular fiber size.

By coalescence is understood the flowing together of small droplets ofliquids so as to form larger droplets. This permits easier and morerapid phase separation.

The problem of the separation of droplets of one liquid from a secondliquid which is immiscible with the first is of frequent occurrence inboth the petroleum industry and the chemical industry. This happensoften in those cases where liquids are contacted with a treating liquid,which is immiscible therewith for the purpose of efiFecting extractionsand/ or chemical conversions. Generally, the two liquids are thoroughlymixed, which produces a fine dispersion which may be of the treatingliquid in the liquid to be treated. After the contact time required inthe particular application, the dispersion is passed into a settlerwhere, owing to differences in gravity, a large part of the dispersedphase separates in the form of a separate layer of liquid often afteronly a short time. The

separation of the relatively fine droplets, however, in many casesproceeds only exceedingly slowly and this separation is sometimeshampered by the presence of surface-active substances which hampercoalescence.

It is known in the art that in the refining of hydrocarbon mixtures withsulfuric acid an improved phase separation may be achieved by firstthoroughly mixing the hydrocarbons with sulfuric acid, next passing thehydrocarbon-sulfuric acid emulsion formed through a. layer of fibrouspolyolefin, and subsequently achieving phase separation in a settler.According to the known method, the layer of polyolefin fibers, whicheffects coalescence of dispersed liquid, preferably consists ofpolyethylene fibers which (according to the data on packing density,free space and surface area of the fibers) have a diameter of from240-700 microns.

In accordance with the instant invention, it has been found that a muchmore rapid and more efficient coalescence can be effected byapplicatioin of polyolefin fibers with an average diameter of from -100microns or even less, e.g., as small as 3 microns. Contrary toexpectations, dispersions of extremely small droplets of liquid caneasily be caused to coalesce and, consequently, to separate with the useof these very fine fibers, even at relatively high superficialvelocities.

The invention, therefore, relates to a process for separating dropletsof one liquid from a second liquid which is immiscible with the first byfirst passing the liquid mixture through a layer of polyolefin fibersand subsequently eifecting phase separation. It is important that theliquid mixture be passed through a layer of polyolefin fibers of whichthe average fiber diameter is from 5-100 microns.

Suitable fibrous materials according to the invention are, in general,fibers of high-molecular weight polyolefins, such as polymers and/ orcopolymers of C -C olefins. These polyolefins have molecular weights offrom 50,000- l,000,000 and preferably of from 100,000-300,000. Of

the aforementioned polyolefins, polypropylene is particularly suitableas a fibrous material, because it meets the high mechanical, physical,and chemical demands.

This is because the fibrous material must meet various requirements.Naturally it must not be too brittle and on the other hand it must besufficiently strong and elastic not to be compressed into an impermeablemass at liquid pressures of normal occurrence. Further, the fiber mustnot, or substantially not, be soluble in the liquids of the system to beseparated, and must likewise not be attacked chemically by theseliquids.

A further advantage of polypropylene is that it can be spun to thedesired fiber diameter in a simple manner.

The polyolefin fibers according to the invention can be applied both inthe form of loose fibers .and in a processed form, for instance as felt.Preferably the fiber diameter is from 10-60 microns. The length of thepolyolefin fibers is at least 10 times and preferably at least 100 timesthe fiber diameter.

It is observed that the thickness of the layer of fibers may varybetween wide limits. In general with application of loose fibrousmaterial a somewhat larger layer thickness will be required than withuse of, for instance, felt, because the latter as a rule will possess amore homogeneous texture. For loose fibrous material the layer thicknessin general varies from 5-100 centimeters and preferably from 20-50centimeters. For processed fibers, such as felt, the layer thicknessgenerally is from 1-30 centimeters and preferably from 2-10 centimeters.

As regards the packing density of the fibrous layer, it is stated thatalthough the present fine fibers permit the application of a relativelyhigh density, the fibrous layer nevertheless preserves a very highpercentage of free space. High packing densities are in advantagebecause they very much contribute to fine droplets being caught and thusbeing made to coalesce.

The free space in the fibrous material in general is from -98% andpreferably from 88-95%. The large free space in the fibrous material isan advantage, because it permits easy handling of, inter alia, systemswith a relatively high concentration of dispersed phase.

The velocities with which the liquids to be coalesced are passed throughthe fibrous layer, expressed as the superficial velocity are generallyfrom 0.1-10 centimeters per second and preferably from 0.5-6 centimetersper second. What velocity will be chosen in a specific case will depend,.among other factors, on the nature of the liquid mixture to beseparated. Thus it will be desirable with very small droplet sizes and/or with a low surface tension between the liquids to be separated toapply relatively low superficial velocities.

By superficial velocity is intended the velocity of the liquid in cubiccentimeters per second divided by the crosssectional area of the fiberlayer applied in square centimeters.

If desired, the coalescence may be effected in two or more steps, forintance by passing the liquid to be separated successively through twoor more columns, each of which is provided with a layer of fibrousmaterial. An embodiment of this type may be advantageous in cases wherethe liquid to be separated contains a high concentration of dispersedphase or where the dispersion consists of droplets varying in size. Thelarge droplets formed by coalescence may then by settling or otherwisebe separated before the liquid mixture is passed through a followingfiber layer.

It is observed that the filling of, for instance, a cylindrical columnwith loose fibrous material to form a homogeneous bed requires a certainskill. A homogeneous filling is desirable to prevent the occurrence of anonuniform flow of the liquids over the cross-sectional area of thecolumn. Further, it is essential that the fibers fit the column is quiteeasy using processed fibrous material,

which is preferably applied in the form of thick mats of felt becausethe required height can be obtained simply by stacking the felt matswhich have been cut to match the cross-section of the column. The matscan be cut in such'a manner asto ensure a proper seal against the wallof the column. Alternatively, rolls of felt mat can be stacked, suitablycoaxially with the column and preferably in such a way that theinterstices between the rolls of one layer are covered by the bodies ofthe rolls of a subsequent layer.

In cases where the liquids to be coalesced contain solid impurities, itis recommended that these be previously filtered oflf to preventclogging of the fibrous layer.

The fibrous material will, as a rule, be supported on an appropriatemeans, such as a perforated plate or a wide-mesh screen. On the top, asimilar means may likewise be applied, particularly in the case ofcovering loose fibrous material, because the desired packing density ofthis material can thus easily be obtained and maintained.

For a better distribution of the liquid over the fibrous coalescer bed,there may bearranged within the same column and upstream of this bed alayer of other, preferably granular packing material, such as gravel.This may in certain cases already elfect some coalescing in the liquid.The layer in question may be supported on a plate or screen covering thefibrous bed (as indicated above) so that it precedes the fibrous bedimmediately, or there may be a gap between the bed and the layer, inwhich case the liquid leaving the layer flows through an empty space ofthe column before entering the fibrous bed.

It is also possible to obtain and maintain the desired packing densityof the fibrous bed by dumping a quantity of fairly heavy loose bodies,such as rocks, lumps of metal, gravel, or the like, right on top of thefibrous material (viz without any intervening screen or plate),especially when loose fibrous material is employed. Besides providingthe required compression of the fibrous material, the layer of loosebodies thus formed also serves as a distributing and possiblyprecoalescing means, as has already been discussed above with referenceto a separately supported layer of granular material.

As has been stated hereinbefore, the problem of the separation ofdroplets of one liquid from a second liquid which is immiscible with thefirst is of frequent occurrence. For instance, when extracting certaincomponents from a liquid with the aid of a treating liquid, or whensystems wherein chemical reactions occur in a heterogeneous liquidmedium.

Examples are the treatment of petroleum fractions with caustic solutionor with acids. In the treatment with acids, for instance, kerosene isfirst thoroughly contacted with sulfuric acid. Next, as much acid aspossible is separated in a settler by separation of the layers. Thedroplets of acid that remain behind in the kerosene are now, accordingto the invention, passed through a layer of polyolefin fibers whereuponthe relatively large droplets of acid formed by coalescence areseparated by settling. It is an advantage of the present fibers thatextremely fine droplets of acid also can be removed by coalescence, as aresult of which in a subsequent treatment with caustic, only-orsubstantially only-the acid components dissolved in the kerosene, suchas sulfur dioxide and sulfonic acids, needto be neutralized. This meansa considerable saving in caustic in comparison with embodiments whereconventional means of coalescence are applied.

It is observed that as'a rule it is advantageous first to separate, bysettling or otherwise, the relativelylarge droplets from the liquidmixture to be separated and after that to pass the remaining finedispersion through the layer of polyolefin fibers.

EXAMPLE; I

As. starting material use was made .of ,a .kerosene. obtained bystraight-run distillation, with'avboiling range of from 250 C. (ASTM)and with a mercaptan sulfur content of 129 parts per million.

This kerosene was in a commercial plant continuously introduced into apropeller mixer and thoroughly mixed with a circulating sulfuric acidphase, in thevolume ratio of 1:1. The emulsion thus formed wascontinuously introduced into a settler where the greater part of thedispersed sulfuric acid phase separated off. Part of this commercialstream of kerosene was continuously intro-,

duced into a column, mounted ina vertical position, which was providedwith a layer of polypropylene fibers. The height of this layer was 50centimeters, the diameter 39 centimeters, the fiber diameter Was40'microns and the packing density 110 grams per, liter.

Nine experiments were conducted; the experiments 1 to 6 at a superficialvelocity of 0.5 centimeter per second and the experiments 7 to 9 at 0.9centimeter per second. The kerosene introduced contained a fine dispersion of sulfuric acid droplets, of which the concentration according tothe acid number varied owing to fluctuations in the commercial plant.

The effluent from the coalescer column was introduced 1 into a settlerwhere easy separation=of the acid droplets occurred.

From the results .included in Table I it appears that a substantiallycomplete removal of the sulfuric acid has 7 been obtained at asuperficial velocity of 0.5 centimeter L per second.

Table l Superficial Acid number, milligrams H 50 per liter Experimentvelocity,

N0. centimeters per second Inlet 7 Outlet Removal EXAMPLE ,11

air thoroughly mixed with a circulating caustic phase consisting of 40%KOH; 20% triethylene glycol and 40% Water (percent by weight). Theemulsion formed in the process was continuously introduced into asettlerwhere the greater part of thedispersed caustic phase separated 01f. Partof this commercial stream of gasoline was continuously introduced in acolumn,-mounted in a vertical position, which was provided withia layerof polypropylene fibers. The height of this layer was 50 centimeters,

the, diameter 45 centimeters, the fiber diameter 40=microns and thepacking densityllO gramsper liter.

5 6 Seven experiments were conducted at a superficial ve- Table IVlocity of 1.5 centimeters per second. The gasoline introducjed contamcda fine disperslon of Caustic droplets, of Superficial Suspended waterCoalcscing efliciency, percent which the concentration according to thepotassium concvelocltyy before treatlntznb tent varied owing tofluctuations in the commercial plant. 5 22 3 3 parts per mlnlon microns100/200 microns The efiiuent stream from the coalescer column wasintroduced into a settler where easy separation of the [155 160 9&8 57droplets of caustic occurred. 305 39 From the results included in TableII it appears that 205 O 16 substantially theoretical removal of thecaustic was ob- 1 tamed. 10 Not measured.

Table H For this table, it is apparent that at conditions under which.the fine fibers given excellent results, nothing even SuperficialPotassium clltqntinparls P remotely resembling these results can beobtained with velocity, mllhon Experiment centimeters the coarserfibers; at a temperature velocity which is not Per Sewnd Inlet OutletRemoval even extremely high the efiiciency of the coarser fibers percentalready becomes so low that it is hardly worth while to carry out thetreatment at all. 1. 5 3 0. 05 1 100 We claim as our invention: {2 $328: 8% H88 1. A process for the coalescence of a hazy hydrocarbon 1'5 185'05 1100 oil comprising water dispersed in kerosene which com- 1.5 so0. 05 1 100 prises passing said oil through a layer from about 20 to 2%2382 H88 about 50 centimeters thick of polypropylene fibers having afiber diameter of from about 3 to about 100 microns, 1 Ca. having afiber length at least about 100 times the fiber diameter, wherein saidpolypropylene has a molecular weight of from about 100,000 to about300,000, wherein EXAMPLE III the free space of the layer is from about88 to about 95%, Since the results obtained under favorable conditionsand wherein said oil is passed through the layer at a suall turned outto be almost equally good, so that it is perficial velocity of fromabout 0.5 to about 6 centimeters hardly possible to show any difierencesin results due per second, and subsequently effecting phase separation.to dilferences in the choice of conditions, a number of 2. The processof claim 1 wherein the polypropylene experiments were carried out underconditions at which fibers are in the form of a layer of loose fibers.optimal results could not be obtained, viz. using a thin 3. The processof claim 1 wherein the polypropylene layer of coalescing material, avery fine dispersion and fibers are in the form of felt. at relativelyhigh superficial velocities, in order to show 4. The process of claim 1wherein the liquid mixture is the influence of fiber diameter within thepreferred range passed successively through at least two layers ofpolyof 10-60 microns. propylene fibers and the relatively large dropsformed by The suspension consisted of a haze of 0.5% water incoalescence are separated by sedimentation before the kerosene having anaverage droplet size of 7 microns; 4O liquid mixture is passed through afollowing layer of the height of the coalescing layer was 8 millimeters.polypropylene fibers. Coalescence efliciency was measured by means ofturbidi- 5. The process of claim 1 wherein the layer of polymeterreadings effected before and after treatment. Furpropylene fibers arecovered by a layer of gravel. ther particulars of conditions employedand results ob- 6. A process for the coalescence of a liquid mixture oftained are set out in Table HI. sulfuric acid and hydrocarbon oilcomprising contacting Table III Coalescing efficiency, percentSuperficial Velocity, 9 1% Free space in layer 88% Free space in layercentimeters/Second 15 22 35 5 15 22 35 Microns Mierons Microns MieronsMicrons Microns Microns Microns From this table it is apparent that atany specific value of the superficial velocity employed, a definitemaximum of coalescing efficiency is present at a certain fiber diameterlying within the preferred range.

EXAMPLE IV said liquid mixture with a layer of polyolefin fibers,selected from the group consisting of polymers and copolymers of C -Colefins having a molecular weight of from 50,0001,000,000 and having anaverage fiber diameter of from about 3 to about microns, andsubsequently effecting phase separation.

7. The process of claim 6 wherein the average fiber diameter is fromabout 10 to about 60 microns.

9. The process of claim 6 wherein the fibers consist of polypropylene.

8. The process of claim 6 wherein the fiber length is at least about 10times the fiber diameter.

10. The process of claim 6 wherein the relatively large drops areseparated off by sedimentation from the liquid 7 8 mixture to beseparated prior to passing the remaining dis- 3,098,108 7/ 1963 Preiser2Q8,299X persion through a layer of polyolefin fibers. .7 3,152,19610/1964 Marziani 260-6815- References Cited y the Examiner DELBERT ELGAT Primary Examiner; r l UNITED STATES PATENTS ALPHONSO SULLIVAN, PAUL.M. COUGHLAN, 2,859,260 11/1958 Stiles 260-68162" Examiners.

3,016,345 1/1962 Price 208187

1. A PROCESS FOR THE COALESCENCE OF A HAZY HYDROCARBON OIL COMPRISINGWATER DISPERSED IN KEROSENE WHICH COMPRISES PASSING SAID OIL THROUGH ALAYER FROM ABOUT 20 TO ABOUT 50 CENTIMETERS THICK OF POLYPROPYLENEFIBERS HAVING A FIBER DIAMETER OF FROM ABOUT 3 TO ABOUT 100 MICRONS,HAVING A FIBER LENGTH AT LEAST ABOUT 100 TIMES THE FIBER DIAMETER,WHEREIN SAID POLYPROPYLENE HAS A MOLECULAR WEIGHT OF FROM ABOUT 100,000TO ABOUT 300,000, WHEREIN THE FREE SPACE OF THE LAYER IS FROM ABOUT 88TO ABOUT 95%, AND WHEREIN SAID OIL IS PASSED THROUGH THE LAYER AT ASUPERFICIAL VELOCITY OF FROM ABOUT 0.5 TO ABOUT 6 CENTIMETERS PERSECOND, AND SUBSEQUENTLY EFFECTING PHASE SEPARATION.